The present invention relates to a video communication system and also to a phase or frequency modulator included in such system. The invention is particularly applicable in "freeze frame" transmission of video signals, e.g., for making conference telephone calls or for monitoring security areas, and therefore the invention is described below with respect to this application.
The existing "freeze frame" video communication systems commonly include a TV camera producing a video analog output of the scene to be transmitted, an analog-to-digital converter for digitizing the analog signals, a memory, a digital compression unit, and a modem (modulator-demodulator) for modulating a carrier wave signal before transmission via the telephone line or radio to a receiver. The receiver in such systems includes another modem, a decompression unit, a memory, and an digital-to-analog converter for reconverting the digital signals back to analog signals before fed to a TV display unit. Such systems, however, are quite costly particularly because of the need for a digital-compression unit in the transmitter, and a digital-decompression unit in the receiver.